Baltimore police said Friday afternoon that they have charged a sergeant with misconduct in connection with a state delegate's marriage proposal, in which on-duty city officers using a police boat and helicopter staged a mock raid of a boat.

After the Aug. 7 proposal gained widespread attention, Del. Jon S. Cardin, a Democrat, reimbursed the Police Department $300 and the department launched an inquiry. Cardin has refused to answer questions about how police became involved, and on Friday police provided few answers beyond disclosing that an allegation of misconduct had been sustained against an unnamed supervisor in the Special Operations Section.

"The investigation found that units within the Special Operations Section often participate in activities to project a positive public image and build relations within the community," police said in a statement. "However, in this instance, the supervisor ... who approved the use of marine unit resources for this non-public purpose improperly exercised his discretion."

Police said that the stunt lasted no longer than three minutes and that the officers were within their assigned area of patrol and remained available to respond to calls for service.

The misconduct charge was brought before an internal charging committee, which sustained the allegation. The officer now has the option of bringing the charge before an internal trial board.